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Genetics

In this lesson, students will learn about genetics and heredity through Punnett squares. They will predict outcomes of genetic crosses, calculate probabilities of genotypes and phenotypes, and understand the concepts of genes, traits, alleles, dominance, and phenotype-genotype relationship.

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Genetics

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  1. Genetics The study of heredity

  2. Today’s Objective: • Using Punnett squares, students will predict the outcomes of 4 different genetic crosses and calculate the probability of each possible genotype and phenotype.

  3. How are we going to get there • Twins! • Gene vs Trait vs Allele • Who was GregorMendal? • Dominant and Recessive • Heterozygous vs. Homozygous • Phenotype vs. Genotype

  4. Work this out on the left side of your guided notes Looking at these twins… What are some characteristics that are the same? What are some characteristics that are different? How can they be so different and still have the same parents? http://www.youtube.com/watch?v=eRdcL2qKt6k

  5. Terms to Know • Genes: the chemicalfactors that determine traits (coded instructions or pieces of DNA) • Trait: a specific characteristic (like eye color or plant height) that varies, or changes, from one individual to another

  6. Terms to Know • Allele: Different forms (like flavors) of a gene. All organisms have two alleles for each trait (one that originally came from the mother and one from the father) • Example- • Gene: ATCGCTATAGCAGAT • Trait: seed color • Alleles: yellow or green

  7. Work this out on the left side of your notebook What traits and alleles do you see? Trait Alleles

  8. Speed Round (A) • Blue eyes • Smooth Skin • Hair Color • Size • Sharp teeth (A) (T) (T) (A)

  9. Gregor Mendel • European monk • Studied traits of pea plants in the mid 1800’s • Considered the father of modern genetics https://www.youtube.com/watch?v=Mehz7tCxjSE

  10. Mendel’s Conclusions • Biological Inheritance is determined by factors (genes) passed down from generation to generation. • Principle of Dominance: Some alleles are DOMINANT and others recessive.

  11. Sometimes your alleles are Bullies!!!!

  12. Dominant allele that masks the expression of another the one that presents itself or the one you see. The bully! Represented by capital letters (A, R)

  13. Recessive- allele that is expressed only if both parents contribute it the victim! Represented by lower case letters (a, r)

  14. Homozygous: two identical alleles • BB, TT = homozygous dominant • bb, tt= homozygous recessive • Homozygous = true-breeding = purebred

  15. Purebred: offspring of crosses between parents with the same alleles

  16. Heterozygous: two different alleles • Bb, Tt= heterozygous • Heterozygous = hybrid

  17. Hybrids: offspring of crosses between parents with different alleles

  18. Any Questions??

  19. Which ones are HOMOZYGOUS, and which ones are HETEROZYGOUS?

  20. Genotype: Genetic makeup – exactly what alleles are present • examples-Tt, BB, aa • Phenotype: Physical characteristics – what the organism looks like • Examples-tall, blue eyes, curly hair http://www.thetech.org/genetics/index.php

  21. Speed Round Are the following heterozygous or homozygous? BB, aa homozygous 2. If B= Brown fur and b= white fur, what would be the color of an individual with the genotype Bb Brown 3. Is B dominant or recessive? dominant 4. Is “blue eyes” a genotype or a phenotype? phenotype 5. Which allele is usually expressed- the dominant one or the recessive one? the dominant one

  22. Turn to page 267 Punnett Squares • Probability: chance that something will happen, can be used to predict outcomes of genetic crosses because alleles segregate RANDOMLY, just like flipping coins • Punnett Squares: can be used to predict and compare genetic variations that happen in a cross

  23. Fill in the following monohybrid Punnett square if parents are FF and Ff: F F F F F F F F F f f f f f

  24. Punnett Squares • Step #1: Make a key • Step #2: What do we know about the parents? Highlight the information. • Step #3: figure out the parents’ genotypes (the letters) • Step #4: fill out the Punnett Square

  25. In mice, if B=Brown fur and b= white fur, what are the possible genotypes and phenotypes of the offspring of a heterozygous Brown mouse and a homozygous recessive (white mouse)? Possible genotypes: Possible phenotypes:

  26. In this same cross, what are the chances of having a white mouse? What about a brown mouse? Possibility of white offspring: Possibility of brown offspring:

  27. Bikini Bottom Genetics

  28. Speed Round Which ones are heterozygous? BB, Aa, aa, Tt Heterozygous = AaTt 2. If B= Brown fur and b= white fur, what would be the color of an individual with the genotype Bb Brown 3. Is “b” a dominant allele or a recessive allele? recessive 4. Is “purple ears” a genotype or a phenotype? phenotype 5. Which allele is usually expressed- the dominant one or the recessive one? the dominant one

  29. More Speed Round Qs If B= Brown fur, and b= white fur,what is the homozygous dominant genotype? BB 2. What is the heterozygous phenotype? Brown fur 3. What is the homozygous recessive phenotype? white fur 4. What is the heterozygous genotype? Bb 5. What is the homozygous recessive genotype? bb

  30. Let’s get to the part about SEX… • Humans have 46 chromos, or 23 homologous pairs • 22 are AUTOSOMES, or regular chromosomes • Pair #23 = sex chromos XX or XY • XX = female genotype • XY = male genotype • (if there’s a Y, it’s a GUY!!) Karyotype = Picture of all the chromosomes paired up

  31. Work this out on the left side of your notebook When Victoria Beckham got pregnant for the 4th time, she thought it was impossible that she would have a girl (she already had three boys!) Was she wrong? Use a Punnett square to explain your answer…

  32. It’s a GIRL!

  33. Sex determination:

  34. Speed Round: • 1.What are the sex chromosomes? • X and Y • 2. What are the chances of a child being male? Female? • 50/50- ALWAYS • 3. Who determines the sex of the child? Mom? Or Dad? • Dad, because ½ of Dad’s sperm carry a Y and ½ carry an X • 4. What is the female genotype? • XX • 5. What is the male genotype? • XY

  35. However… • There are many exceptions to Mendel’s principles. • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes

  36. Work this out on the left side of your notebook These flowers both had one red parent and one white parent. Compare the ways in which they inherited their colors from their parents:

  37. More Speed Round Qs If B= Brown fur, and b= white fur,what is the homozygous dominant genotype? BB 2.. What is the heterozygous genotype? Bb 3. . What is the homozygous recessive genotype? bb 4. What is the heterozygous phenotype? Brown fur 5. What is the homozygous recessive phenotype? white fur

  38. Incomplete Dominance • Neither allele is completely dominant over the other Example: RR x WW = RW 3 phenotypes • Red flowers (RR) and White flowers (WW) make Pink flowers (RW)

  39. Make a key! INCOMPLETE DOMINANCE In flowers RR = WW = RW =

  40. Work this out on the left side of your notebook What are the genotypes and phenotypes of a cross between a red (RR) flower and a white (WW) flower if flower color is incompletely dominant??

  41. Work this out on the left side of your notebook What are the genotypes and phenotypes of a cross between a pink flower and a red flower if flower color is incompletely dominant??

  42. Work this out on the left side of your notebook What are the genotypes and phenotypes of a cross between a two pink flowers if flower color is incompletely dominant??

  43. Codominance • Both alleles contribute to the phenotype • Both dominant phenotypes show up together in the heterozygous form • RR x WW = RW (red and white TOGETHER) • No Blending!!

  44. Codominance or Incomplete Dominance?

  45. If fish color were incompletely dominant instead of codominant, what color would the offspring be?

  46. Make a key! CODOMINANCE in fish RR = BB = BR =

  47. Work this out on the left side of your notebook Codominance: If a blue fish (BB) is crossed with a red fish (RR), what percentage of their offspring will be patchwork (BR)

  48. Work this out on the left side of your notebook Codominance: If two patchwork fish (BR) mate, what genotypes and phenotypes will the offspring have?

  49. Is this chicken an example of Codominance or Incomplete Dominance? How do you know? Explain using scientific language

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